1. Field of the Invention
The present invention relates to an image processing apparatus and method thereof and, more particularly, to settings of color processing parameters.
2. Description of the Related Art
In recent years, the prevalence of digital cameras has facilitated digitization of photos. As a result, the frequency of handling photo image data on personal computers is on the rise. Furthermore, the prevalence of ink-jet printers now allows easy photo printing from photo image data. Moreover, the prevalence of application software used to correct and modify images allows to freely execute image processing on personal computers. For example, color adjustment is made by adding cyan as a complementary color to a reddish image, or correction is applied to the brightness of an image including a dark object image due to backlight to increase the brightness of the object image.
In monochrome printing, the tone is very important for the finish of a print. In monochrome printing, a warm black tone of an entirely yellowish image, a cold black tone of an entirely bluish image, and the like are generally known. That is, the tone to which the gray balance is biased largely changes the impression of a print image. For this reason, a system which can easily adjust the gray balance to the tone that the user wants is demanded.
In recent years, the color reproductivity of printers has improved to allow color adjustment with high precision. The user sets parameters required to perform color adjustment (color adjustment parameters) and can finish a print image to have a desired tone. However, it is very difficult to simultaneously set a plurality of color adjustment parameters.
As a method of setting a desired tone, a plurality of color adjustment parameters are set in a plurality of levels, and color processing is applied to a source image (original image) using combinations of color adjustment parameters of respective levels. A plurality of images processed based on different combinations of color adjustment parameters are laid out on one page and are printed. The user observes respective images (index images) of a sample print, and selects an index image with a desired tone, thus setting the color adjustment parameters.
Upon printing an image without color adjustment, a print image with color reproduction unique to a printer is obtained. The color reproductivity largely varies depending on printer models, and also varies depending on environmental conditions (temperature, humidity, and the like) and the degree of wear of a printhead. Furthermore, the color reproductivity largely varies depending on the combinations of print paper types and color materials (inks or toners). In other words, in order to realize the color reproductivity that the user wants, color adjustment according to the printer models, environments, print paper types, and color materials is indispensable.
FIG. 1 shows an example of a user interface (UI) of application software or a printer driver, which has a function of setting a plurality of color adjustment parameters. With this function, the user can adjust the tone of an image to obtain a print image with a desired tone according to the printer models, environments, print paper types, and color materials. The UI shown in FIG. 1 has a slider bar used to adjust color in the direction of red or cyan, a slider bar used to adjust color in the direction of green or magenta, and a slider bar used to adjust color in the direction of blue or yellow.
The user adjusts the tone of a print image by operating the sliders shown in FIG. 1. The user then instructs the application software or printer driver to output a sample print as a target for the tone adjustment result. The application software or printer driver outputs a sample print to have an image to which the color adjustment parameters designated by the operations of the slider bars are applied as a reference image. Therefore, index images which are processed based on the specific combinations of the color adjustment parameters set in a plurality of levels to have the current color adjustment parameters as the center are arranged around the reference image.
The user observes the sample print to select an index image with a desired tone, and sets the color adjustment parameters by, e.g., inputting the number of the index image of interest to the UI. When there is no index image with the tone that the user desires, the color adjustment parameters that the user desires fall outside the range of the combinations of the color adjustment parameters used to output the sample print. In this case, the user selects an index image which has a tone approximate to the desired tone, and sets the color adjustment parameters by, e.g., inputting the number of that index image. After that, the user instructs to output a sample print again. As a result, the image to which the set color adjustment parameters are applied is used as a reference image, and a sample print including index images obtained by changing the color adjustment parameters to have that image as the center can be output.
Japanese Patent Laid-Open No. 2002-027222 discloses a technique which determines the color adjustment direction on a chromaticity coordinate plane after a primary sample print, and then outputs a secondary sample print based on a fine adjustment level count. That is, the primary sample print uses a two-dimensional layout based on chromaticity coordinate parameters a* and b*. The secondary sample print after the designation of the color adjustment direction (hue value) uses a two-dimensional layout based on lightness L* and saturation S as parameters. However, since this method uses the layout based on the lightness and saturation to obtain the secondary sample print, the hue value must be accurately set in the stage of the primary sample print. In other words, the secondary sample print cannot print index images obtained by finely adjusting the hue value. For this reason, the user searches index images with the fixed hue values for one with a desired tone.
Japanese Patent No. 2773188 discloses sample printing (mosaic monitor mode) in a digital color copying machine. This technique performs sample printing by calculating color adjustment parameters of a plurality of levels upon applying predetermined arithmetic operations to reference values. Then, this technique performs sample printing again by setting the color adjustment parameters of the index image selected by the user as reference values for the next color adjustment arithmetic operations. However, Japanese Patent No. 2773188 does not describe sample printing that considers so that the user can easily recognize the hue and saturation values, and cannot easily set the color adjustment parameters in association with the hue and saturation values.
With this technique, when the user selects an index image corresponding to the maximum values of the color adjustment parameters, these maximum values of the color adjustment parameters are set as reference values. In this case, the arrangement of index images on a sample print to be printed again may not be easy for the user to see, and a measure against such selection is not disclosed.